The present invention relates generally to a current transformer which is terminated in an active load having virtual short circuited input for developing an output voltage from the load which is proportional to the current in the transformer and, in particular, to an improved apparatus and method of altering, in the load, the phase angle of the output voltage relative to the transformer current by compensating for the phase shift in the transformer current.
In U.S. Pat. No. 3,815,012 to Miran Milkovic, the inventor of the present invention, and assigned to the assignee of the present invention, there is disclosed a circuit having a current transformer terminated in an operational amplifier or active load for providing phase angle alteration of the transformer current to produce an output voltage from the operational amplifier which is proportional to current in the transformer. In that patent, passive circuit elements (eq, resistors and capacitors) are connected between the output terminal and an inverting input terminal of an operational amplifier for effecting a shift in the phase angle between the transformer current and the output voltage produced by the amplifier in response to current in the transformer secondary winding.
While the circuit disclosed in the aforementioned U.S. Pat. No. 3,815,012 patent functions very well, it suffers from a competitive economic standpoint because of its need of the aforementioned passive circuit elements. Thus, a need exists for an active terminated current transformer circuit capable of phase shift compensation of current in the transformer which provides that compensation in a more economical and straight forward fashion.